Adapter for current distributor rail

ABSTRACT

An adapter for joining two current distributor rails together, or supplying or tapping current to or from a rail, comprises a two-part insulating housing, a pair at least of contact assemblies spring-loaded to extend retractable contacts through slots in opposite sides of the housing so as to engage current carrying conductors in the rail(s), when in use, an earthing plate on the housing located to first engage an earthing conductor when the adapter is inserted into a rail, and locking lugs on the adapter to engage slots in the rail.

United States Patent 1191 1111 3,825,879

Hesse 1 July 23, 1974 [5 ADAPTER FOR CURRENT DISTRIBUTOR 3,601,749 8/1971 Hart et al 339/14 R L 3,605,064 9/1971 Routh et al. 339/21 R 3,622,938 ll/l97l Ito et al 339/21 R Inventor: Kurt Hesse, Waterfohr, 2 3,688,240 8/1972 Routh et al. 339/21 R Lemgo-Lippe, Germany {22] Filed: Aug 2" 1972 Primary Examiner-Bobby R. Gay

Assistant Examiner-Robert A. Hafer PP' 277,303 Attorney, Agent, or Firm-Steinberg & Blake [30] Foreign Application Priority Data ABSTRACT Aug. 3, 1971 Austria 6789/71 An adapter for joining two current distributor fails gether, or supplying or tapping current to or from a [521 US. (:1 339/21 R rail, Comprises a -p insulating housing, a p at [51] Int. Cl H01r 9/00 least of Contact assemblies Spring-loaded to extend [58] Fi ld f S h 339/14 R, 21 R, 215 20, tractable contacts through slots in opposite sides of 339/22 B, 23, 24 the housing soas to engage current carrying conductors in the rail(s), when in use, an earthing plate on [56] References Cit d the housing located to first engagean earthing con- UNITED STATES PATENTS ductor when the adapter'is inserted into a rail, and 3,559,146 1/1971 Valtonen 339/14 'lockmg lugs on the adapter to engage Slots m the 3,601,748 8/1971 Hart et a] 339/14 R 3 Claims, 11 Drawing Figures 1 ADAPTER FOR CURRENT DISTRIBUTOR RAIL The present invention concerns an adapter for current distributor rails. The adaptor may either bridge two current distributor rails abutting each other in a straight line, or feed a supply of electrical current to or from the current distributor rails the adapter being of a simple, economical and compact design, easy to operate and havingv a high degree of electrical safety.

According to the present invention there is provided an adapter for current distributor rails, the adapter being capable of bridging two current distributor rails abutting each other or supplying or withdrawing current to or from the current distributor rail, comprising a housing insertable in a receiving space of the current distributor rail or rails a plurality of contact members held within the housing and extending out of the housing to make contact with the current conductors of the distributor rails, the contact members being slidable in the housing, and at least one earth conductor contacting a protective conductor of the current distributor rail before the live rail conductors contact the adapter members the adaptor having holding lugs engaging in securing recesses of the distributor rail to lock the adapter therein when in use.

In a preferred embodiment the adapter has a housing corresponding incross-section to a receiving recess of the rail, with a rectangular three dimensional form, and formed as a hollow body consisting of two halves held together by connecting means.

Located within the housing of the bridging adapter are two relatively opposed displaceable members which are held against the opposing side walls of the housing by at least one pressure element, such as a compression spring, on each of which there are at least two electrically conducting interconnected contact members in contact when in use with the current conductors of the two distributor rails to be interconnected and one holding lug. The two contact parts are preferably formed as a unitary structure with a connecting strap and secured to the displacement member by this strap; it is preferable to provide each displacement member with two superimposed connecting straps each having two contact members provided with a clearance between them in the longitudinal direction of the housing.

The housing of a feeder adapter also contains two relatively opposed displaceable members on each side, urged outwardly by a spring and each having at least one contact member with connecting part; all the contact members are connected by their connecting straps by way of electrical leads, to a coupling member, such as a plug or socket, provided in the housing and accessible from the end of the housing away from the contact members, in which plug or socket a counterpart of an electrical feed conductor is insertable. From the earthing conductor of a housing, an electrical lead also extends to the coupling member. When the adapter is inserted in the rails the contact members and holding lugs thereof are automatically pushed back into the housing and then locate themselves against the conductors or in the rail recesses. The outside of the housing may be provided with holding lugs rigidly secured thereto, instead of the displaceable holding lugs.

The displaceable members with the contact members and the holding lugs may be pushed together from the lower side of the adapter to the longitudinal bi-sector 2 of the adapter, so that it is possible to insert the adapter from the open longitudinal side of the rail.

Embodiments of the invention are illustrated in the accompanying drawing in which:

FIG. 1 is a perspective view of a bridging adapter comprising contact members and holding lugs extending out of the adapter housing on opposed sides of the housing;

FIG. 2 is a perspective view of a feeding adapter comprising contact parts, holding lugs and a front coupling member;

FIG. 3 shows a perspective view of two current conductor rails abutting each other in a straight line with a bridging adapter between them and a feeding adapter at one end of one rail;

FIG. 4 shows a longitudinal section through the bridging adapter taken on the line IIII of FIG. 5;

FIG. 5 is a cross-section through the bridging adapter taken on the line I-I of FIG. 4;

FIG. 6 shows a longitudinal section through the feeding adapter;

FIG. 7 shows a perspective view of a bridging or feeding adapter comprising holding lugs rigidly secured to the outside of the housing;

FIG. 8 is a cross-section through a modified current conducting rail with end view of an alternative embodiment of a bridging adapter; I

FIG. 9 is a side view of the bridging adapter in accordance with FIG. 8; g

FIG. 10 is across-section through the same bridging adapter taken on the line III-III in FIG. 9;

FIG. 11 is an exploded view of the same bridging adapter showing its upper casing part, the sprung contact members and its lower casing part.

In FIG. 1, a bridging adapter 10, constructed in accordance with the present invention and intended for two current distributor rails 12 abutting each other in a straight line, has a feeding adapter 11 for the supply of electrical current to the distributor rails 12 with contact members 16 in housings l3, 14, the adapter being inserted in the receiving space 12a of the rail 12 of the U or C cross section; the contact members 16 are acted upon by spring pressure in the width direction of the rail, and extend out of the side walls 13a, 14a of the housings so as to contact current conductors 15 of the distributor rails 12. The members 16 are movable in the housing l3, 14 during insertion or removal of the adapter. There is an earthing conductor 18 which comes into contact with a protective conductor 17 of the current distributor rails 12 before contact is made between the rail conductor 15 and adapter conductor 16. The adapter has plate-like locating and holding lugs 19 engaging in securing grooves 12b, in the current distributor rail 12 which are accessible from the receiving space 12 a in the two relatively opposed side walls of the rail, the lugs securing the adapter 10, l l, in position in the rail 12. 1

The housings 13,14 of the adapters 10,11 are each formed as a hollow body of plastics material which has a cross-section corresponding to the receiving space 12a of the rail 12 and is formed as a rectangular or square bar; each adapter 10, 11 may be inserted entirely into the receiving space 12a and does not extend, in its inserted position, out of the rail 12 on the open longitudinal side of said rail.

The housings 13, 14 are preferably each divided in a longitudinal direction and is formed of two identical halves which are detachably held together by screws 21', these screws 21 extend through spacer and guide extensions 22 secured to the inside of both halves of the housing (side walls 13a, 14a).

It is also possible to divide the housing 13, 14 in a transverse direction.

In the housing 13 of the bridging adapter there are two relatively opposed displacement members 24 which are held against the opposed side walls 13a by a spring 23, and are capable of being moved towards each other along the guide extensions 22.

There are two electrically conductive interconnected contact members 16, connectable to the conductors 15 of the rails 12 on both sides of the abutting edge 25 of the rail and each extending out of an opening 26 in the side wall 13a of the housing. These members are fixed to each displacement member 24 and are displaceable therewith.

The two contact members 16 of each displacement member 24 are spaced from each other in the longitudinal direction of the rail and the housing and are made as a single metal part to form an electrically conductive connection, with a connecting strap 27. It is preferable to provide each connecting member 24 with two superimposed connecting straps 27 each having two contact members 16 spaced apart from each other in the longitudinal direction of the housing.

The two helical springs 23 press against the displacement members 24 in the region of the opposed contact members 16.

A holding lug l9, engaging a portion of the housing 13 and preferably provided on the longitudinal bisector of the housing, is also rigidly mounted on each displacement member 24, so that it also moves during the displacement of the member 24 and extends out of an opening 26.

Each of the holding lugs 19 has an inclined arcuate clamping surface 19a by which it is clamped automatically in a rail recess 12b.

An earthing plate secured to the top of the housing 13 by a plug or clamp connection is provided as the earthing conductor 18 of the bridging adapter 10, said plate being provided with at least two resilient contact lugs 18a making contact with the protective conductors 17 of the abutting rails 12; this earthing plate 18 is secured in grooves, in the halves of the housing.

The feeding adapter 11 (FIG. 6) also has a housing 14 formed of two halves detachably held together by screws 21.

There are two relatively opposed, plate-shaped, displacement members 24 arranged in the longitudinal end portion of the housing, occupying a portion of the length of the housing and held against the side walls 14a of the housing by a spring 23.

On the displacement members 24 there are contact members 16 fixed in position. Each contact member 16 has a connecting lug 28 by which it is connected to an electrical lead 29 and thence to a plug or socket member 30 inserted in the end of the housing remote from the contact members 16 and secured therein. Two superimposed contact members 16 are provided at one end of the housing and extend out of the housing 14 through respective openings 26. Each has a connecting member 28 directed towards the opposite end of the housing, and an electical lead 29 extends from each connecting member 28 and from the earthing member 18 to the coupling member 30.

Each of the two plate-shaped connecting members 24 is also provided with respective holding lugs 19 located, when viewed in the longitudinal direction of the housing, between the contact members 16 and the coupling member 30. The earthing conductor 18 of the adapter 11 is also formed as an earthing plate, but provided with only one resilient contact lug 18a.

The contact members 16 of the adapters 10,11 are also plate-shaped and taper in width towards their free ends.

The adapter 10,11 shown in FIG. 7 has a housing 13, 14 to the outside of whose walls 13a, 14a the holding straps 20 are rigidly secured or they may be integral with the housing; the two holding straps 20 extend over the entire length of the housing.

The bridging and feeding adapters 10,11 may be inserted in the longitudinal direction of a rail from one end thereof, the resilient contact members 16 and the similarly resiliently mounted holding lugs 19 being partially pushed back into the housing 13, 14 as they strike against the side walls of the rail, and are then pushed outwardly by their springs against the current conductors 15, or inserted in the grooves 12b. In view of the rigid construction of the holding lugs 20 only the contact members 16 are inserted in the rail 12.

The bridging adapter 10 is inserted into the front end of one rail 12 by half its length for the electrical connection of two abutting rails 12 and then the other rail is slipped on the half of the adapter extending out of the rail 12.

The feeding adapter 11 is inserted in one end of a current distributing rail 12 and then, by the connection of its coupling member 30 with a corresponding coupling member of an electrical current supply line, electrical connections with the mains supply are effected so that all current distributor rails electrically connected together by means of bridging adapters 10 are fed by this feeding adapter 11.

Instead of front insertion into the rails 12, the adapters 10, 11 may also be inserted into the rails 12 from an open longitudinal side of the rail. Each displacement member 24 is provided with an actuating extension 31 accessible from the lower side of the housing 13, 14 opposed to the earthing plate 18 displaceable by a tool such as a screwdriver in the direction of the centre of the housing, said extension 31 having a recess 32 for the tool so that, by pressing the two actuating members 31 together towards the longitudinal bisector of the housing, the two displacement members 24, with contacts 16 and holding straps 19, are drawn into the housing 13,14. The two attachments 31 are relatively displaced in the longitudinal direction of the housing. The openings 32 in the two actuating attachments 31 for the tool are accessible through slots 33 in the bottom of the housing.

For polarising (correct direction of insertion) the adapters 10,11 an upper longitudinal edge of each housing or both upper longitudinal edges thereof may be provided with a bevelled or rounded portion 34 cooperating with a corresponding surface on the rails 12, thus ensuring electrically correct insertion of the adapter 10,11.

In the modified embodiment (FIGS. 8-11) of a current distributor rail 35 with a bridging adapter 36, this adapter 36 is inserted in the receiving space 35a of the current distributor rail 35 at the open ends of the rail.

The casing of this modified bridging adapter is in two parts and is provided with an upper cover plate 37, which has two end overlaps 37a, 37b forming connecting parts with the lower part 45 of the same casing. Spring hooks 38a, 38b project downwards from these overlaps 37a, 37b and engage in apertures 46 in the lower part 45, hence detachably connecting these two parts with one another. A central partition 39 forms an abutment for the compression springs 43 of the live electric terminal plates 42, which slide in slots 41 of retaining blocks 40a, 40b. At their inner ends these electric terminal plates 42 are bent over to form retaining strips 42a to prevent them from falling out.

When in use, these electric terminal plates 42 connect conductors 52 of adjacent current distributor rails 35, the rails being secured in an insulating body 55. To hold the lower part 45 relative to the cover plate 37, supports 56 are slipped into a position in which their edges 56a engage grooves 37c on the underside of the cover plate 37. Apertures 57 are left open in the lower part 45, above the projections 49 and the cover plate 37, through which to release the hooks 38a, 38b a screwdriver or the like may be inserted.

part with cover plate 37 and retaining blocks 40a, 40b

is inserted, is provided with laterally projecting retaining lugs 47 which engage in grooves 53 in the current distributor rail 35 and retain the bridging adaptor 36 in the rail 35. Below one retaining lug 47 there is a spring earth conductor strip 48 (resilient at the free ends, whilst being centrally fixed to the casing) in front of which a slot 48a is formed, permitting connection between the protective conductors 54 of two adjacent current distributor rails. On the side walls of the lower part 45 there are projections 49 which retain tightening screws 50 which tighten a connection between current conductor rail 35 in the region of the webs 51, and the bridging adapter 36.

I claim:

1. In an adapter for establishing electrical contact with a plurality of longitudinally extending conductors of a current distributor rail which has a hollow interior at which said conductors are accessible with at least two of said conductors respectively accessible from the interior of said rail at opposed sides thereof and with a third conductor which is accessible at the interior of said rail being a ground conductor, hollow housing means having a cross sectional size and configuration for entering into the interior of said rail, said housing means having a pair of opposed side walls respectively formed with a pair of elongated slots passing therethrough, said housing means carrying a pair of lug means respectively projecting from said side walls of said housing means to be received in grooves at opposed sides, respectively, of said rail and accessible in the interior thereof, said lug means when situated in said grooves locating said slots respectively in alignment with said two conductors extending substantially parallel thereto, a pair of contact members situated in the interior of said housing means and respectively having relatively thin, flat contact plate portions extending freely through said slots outwardly beyond said side walls of said housing means, respectively, where said contact plate portions respectively terminate in periph eral contact edges, said contact members being supported by said housing means for free unobstructed movement transversely of said side walls through said slots thereof, spring means situated in the interior of said housing means substantially in alignment with said contact plate portions and acting on said contact members for urging said contact plate portions thereof outwardly from the interior of said housing means into engagement at said contact edges with said two conductors when said pair of lug means are respectively situated in said grooves, respectively, and ground contact means carried by said housing means at the exterior thereof for engaging said third conductor prior to engagement of said contact plate portions with said two conductors, respectively, when said housing means is introduced into the interior of said rail, said housing means having a pair of opposed end walls which are perpendicular to said slots and a third pair of opposed walls which are parallel to said slots and extend between said side walls and end walls, said side walls each being formed with a pair of said slots which are parallel to and coextensive with each other with each of said slots in each side wall being situated between the other slot and one of said third walls, and four of said contact plate portions respectively extending freely through said slots for respectively engaging at their contact edges four conductors accessible at the interior of said rail when said lug means are respectively situated in said grooves, the pair of slots of each side wall being situated at the region of one of said end walls and each side wall being formed with an additional pair of slots respectively aligned with the first-mentioned pair of slots thereof and situated at the region of the other of said end walls, additional contact plate portions respectively extending through said additional slots, a pair of elongated electrically conductive connecting means situated in the interior of said housing means adjacent each of said side walls thereof with each of said electrically conductive connecting means being fixedly connected with a pair of contact plate portions respectively situated adjacent said end walls in alignment with each other, and said spring means having portions respectively situated adjacent said end walls of said housing means substantially in alignment with all of said contact plate portions for acting on all of the contact members to urge said plate portions thereof outwardly through said slots, said housing means including an interior wall situated substantially midway between and extending parallel to said side walls, and said spring means including a plurality of compression springs equal to the number of contact plate portions and respectively situated in alignment therewith between said interior wall and said sidewalls.

2. In an adapter for establishing electrical contact with a plurality of longitudinally extending conductors of a current distributor rail which has a hollow interior at which said conductors are accessible with at least two of said conductors respectively accessible from the interior of said rail at opposed sides thereof and with a third conductor which is accessible at the interior of said rail being a ground conductor, hollow housing means having a cross sectional size and configuration for entering into the interior of said rail, said housing means having a pair of opposed side walls respectively formed with a pair of elongated slots passing therethrough, said housing means carrying a pair of lug means respectively projecting from said side walls of said housing means to be received in grooves at opposed sides, respectively, of said rail and accessible in the interior thereof, said lug means when situated in said grooves locating said slots respectively in alignment with said two conductors extending substantially parallel thereto, a pair of contact members situated in the interior of said housing means and respectively having relatively thin, flat contact plate portions extending freely through said slots outwardly beyond said side walls of said housing means, respectively, where said contact plate portions respectively terminate in peripheral contact edges, said contact members being supported by said housing means for free unobstructed movement transversely of said sidewalls through said slots thereof, spring means situated in the interior of said housing means substantially in alignment with said contact plate portions and acting on said contact members for urging said contact plate portions thereof outwardly from the interior of said housing means into engagement at said contact edges with said two conductors when said pair of lug means are respectively situated is said grooves, respectively, and ground contact means carried by said housing means at the exterior thereof for engaging said third conductor prior to engagement of said contact plate portions with said two conductors, respectively, when said housing means is introduced into the interior of said rail, said housing means having a pair of opposed end walls which are perpendicular to said slots and a third pair of opposed walls which are parallel to said slots and extend between said side walls and end walls, said side walls each being formed with a pair of said slots which are parallel to and coextensive with each other with each of said slots in each side wall being situated between the other slot and one of said third walls, and four of said contact plate portions respectively extending freely through said slots for respectively engaging at their contact edges four conductors accessible at the interior of said rail when said lug means are respectively situated in said grooves, the pair of slots of each side wall being situated at the region of one of said end walls and each side wall being formed with an additional pair of slots respectively aligned with the first-mentioned pair of slots thereof and situated at the region of the other of said end walls, additional contact plate portions respectively extending through said additional slots, a pair of elongated electrically conductive connecting means situated in the interior of said housing means adjacent each of said side walls thereof with each of said electrically conductive connecting means being fixedly connected with a pair of contact plate portions respectively situated adjacent said end walls in alignment with each other, and said spring means having portions respectively situated adjacent said end walls of said housing means substantially in alignment with all of said contact plate portions for acting on all of the contact members to urge said plate portions thereof outwardly through said slots, a pair of support means situated in the interior of said housing means respectively adjacent said side walls thereof with each support means supporting the four contact plate portions at each side wall, and said spring means including only a pair of compression springs extending freely between and pressing against said pair of support means at the region of each end wall for urging all of said contact plate portions outwardly.

3. The combination of claim 2 and wherein said pair of lug means are respectively carried by said pair of support means for movement therewith in response to the action of said springs, and said pair of side walls of said housing means respectively being formed with slots through which said pair of lug means respectively extend. 

1. In an adapter for establishing electrical contact with a plurality of longitudinally extending conductors of a current distributor rail which has a hollow interior at which said conductors are accessible with at least two of said conductors respectively accessible from the interior of said rail at opposed sides thereof and with a third conductor which is accessible at the interior of said rail being a ground conductor, hollow housing means having a cross sectional size and configuration for entering into the interior of said rail, said housing means having a pair of opposed side walls respectively formed with a pair of elongated slots passing therethrough, said housing means carrying a pair of lug means respectively projecting from said side walls of said housing means to be received in grooves at opposed sides, respectively, of said rail and accessible in the interior thereof, said lug means when situated in said grooves locating said slots respectively in alignment with said two conductors extending substantially parallel thereto, a pair of contact members situated in the interior of said housing means and respectively having relatively thin, flat contact plate portions extending freely through said slots outwardly beyond said side walls of said housing means, respectively, where said contact plate portions respectively terminate in peripheral contact edges, said contact members being supported by said housing means for free unobstructed movement transversely of said side walls through said slots thereof, spring means situated in the interior of said housing means substantially in alignment with said contact plate portions and acting on said contact members for urging said contact plate portions thereof outwardly from the interior of said housing means into engagement at said contact edges with said two conductors when said pair of lug means are respectively situated in said grooves, respectively, and ground contact means carried by said housing means at the exterior thereof for engaging said third conductor prior to engagement of said contact plate portions with said two conductors, respectively, when said housing means is introduced into the interior of said rail, said housing means having a pair of opposed end walls which are perpendicular to said slots and a third pair of opposed walls which are parallel to said slots and extend between said side walls and end walls, said side walls each being formed with a pair of said slots which are parallel to and coextensive with each other with each of said slots in each side wall being situated between the other slot and one of said third walls, and four of said contact plate portions respectively extending freely through said slots for respectively engaging at their contact edges four conductors accessible at the interior of said rail when said lug means are respectively situated in said grooves, the pair of slots of each side wall being situated at the region of one of said end walls and each side wall being formed with an additional pair of slots respectively aligned with the first-mentioned pair of slots thereof and situated at the region of the other of said end walls, additional contact plate portions respectively extending through said additional slots, a pair of elongated electrically conductive connecting means sItuated in the interior of said housing means adjacent each of said side walls thereof with each of said electrically conductive connecting means being fixedly connected with a pair of contact plate portions respectively situated adjacent said end walls in alignment with each other, and said spring means having portions respectively situated adjacent said end walls of said housing means substantially in alignment with all of said contact plate portions for acting on all of the contact members to urge said plate portions thereof outwardly through said slots, said housing means including an interior wall situated substantially midway between and extending parallel to said side walls, and said spring means including a plurality of compression springs equal to the number of contact plate portions and respectively situated in alignment therewith between said interior wall and said sidewalls.
 2. In an adapter for establishing electrical contact with a plurality of longitudinally extending conductors of a current distributor rail which has a hollow interior at which said conductors are accessible with at least two of said conductors respectively accessible from the interior of said rail at opposed sides thereof and with a third conductor which is accessible at the interior of said rail being a ground conductor, hollow housing means having a cross sectional size and configuration for entering into the interior of said rail, said housing means having a pair of opposed side walls respectively formed with a pair of elongated slots passing therethrough, said housing means carrying a pair of lug means respectively projecting from said side walls of said housing means to be received in grooves at opposed sides, respectively, of said rail and accessible in the interior thereof, said lug means when situated in said grooves locating said slots respectively in alignment with said two conductors extending substantially parallel thereto, a pair of contact members situated in the interior of said housing means and respectively having relatively thin, flat contact plate portions extending freely through said slots outwardly beyond said side walls of said housing means, respectively, where said contact plate portions respectively terminate in peripheral contact edges, said contact members being supported by said housing means for free unobstructed movement transversely of said sidewalls through said slots thereof, spring means situated in the interior of said housing means substantially in alignment with said contact plate portions and acting on said contact members for urging said contact plate portions thereof outwardly from the interior of said housing means into engagement at said contact edges with said two conductors when said pair of lug means are respectively situated is said grooves, respectively, and ground contact means carried by said housing means at the exterior thereof for engaging said third conductor prior to engagement of said contact plate portions with said two conductors, respectively, when said housing means is introduced into the interior of said rail, said housing means having a pair of opposed end walls which are perpendicular to said slots and a third pair of opposed walls which are parallel to said slots and extend between said side walls and end walls, said side walls each being formed with a pair of said slots which are parallel to and coextensive with each other with each of said slots in each side wall being situated between the other slot and one of said third walls, and four of said contact plate portions respectively extending freely through said slots for respectively engaging at their contact edges four conductors accessible at the interior of said rail when said lug means are respectively situated in said grooves, the pair of slots of each side wall being situated at the region of one of said end walls and each side wall being formed with an additional pair of slots respectively aligned with the first-mentioned pair of slots thereof and situated at the region of thE other of said end walls, additional contact plate portions respectively extending through said additional slots, a pair of elongated electrically conductive connecting means situated in the interior of said housing means adjacent each of said side walls thereof with each of said electrically conductive connecting means being fixedly connected with a pair of contact plate portions respectively situated adjacent said end walls in alignment with each other, and said spring means having portions respectively situated adjacent said end walls of said housing means substantially in alignment with all of said contact plate portions for acting on all of the contact members to urge said plate portions thereof outwardly through said slots, a pair of support means situated in the interior of said housing means respectively adjacent said side walls thereof with each support means supporting the four contact plate portions at each side wall, and said spring means including only a pair of compression springs extending freely between and pressing against said pair of support means at the region of each end wall for urging all of said contact plate portions outwardly.
 3. The combination of claim 2 and wherein said pair of lug means are respectively carried by said pair of support means for movement therewith in response to the action of said springs, and said pair of side walls of said housing means respectively being formed with slots through which said pair of lug means respectively extend. 